Continuity and change - Reproduction

Asexual reproduction involves a single parent and produces offspring that are genetically identical to the parent (clones). This occurs through processes like binary fission, budding, or vegetative propagation.

Sexual reproduction involves the fusion of two haploid ($n$) gametes to form a diploid ($2n$) zygote, ensuring genetic variation within a population.

Meiosis is a reduction division where the chromosome number is halved from diploid ($2n$) to haploid ($n$). It introduces variation via crossing over in Prophase I and independent assortment in Metaphase I.

Genetic variation in gametes can be calculated using the formula $2^n$, where $n$ is the haploid number of chromosomes.

Human reproduction is regulated by the endocrine system. The menstrual cycle involves hormones from the hypothalamus (GnRH), anterior pituitary (FSH and LH), and ovaries (Estrogen and Progesterone).

Fertilization in humans typically occurs in the fallopian tube (oviduct). The resulting zygote undergoes mitosis to become a blastocyst before implanting in the endometrium.

The placenta is a specialized organ that facilitates the exchange of nutrients, gases, and wastes between maternal and fetal blood without the two blood supplies mixing directly.

External fertilization occurs outside the body (common in aquatic species like fish and amphibians), while internal fertilization occurs inside the female reproductive tract (common in terrestrial animals).